US20160300628A1 - Compact nuclear reactor with integral steam generator - Google Patents
Compact nuclear reactor with integral steam generator Download PDFInfo
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- US20160300628A1 US20160300628A1 US15/156,114 US201615156114A US2016300628A1 US 20160300628 A1 US20160300628 A1 US 20160300628A1 US 201615156114 A US201615156114 A US 201615156114A US 2016300628 A1 US2016300628 A1 US 2016300628A1
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Images
Classifications
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- G—PHYSICS
- G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
- G21C—NUCLEAR REACTORS
- G21C1/00—Reactor types
- G21C1/32—Integral reactors, i.e. reactors wherein parts functionally associated with the reactor but not essential to the reaction, e.g. heat exchangers, are disposed inside the enclosure with the core
- G21C1/322—Integral reactors, i.e. reactors wherein parts functionally associated with the reactor but not essential to the reaction, e.g. heat exchangers, are disposed inside the enclosure with the core wherein the heat exchanger is disposed above the core
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F22—STEAM GENERATION
- F22B—METHODS OF STEAM GENERATION; STEAM BOILERS
- F22B1/00—Methods of steam generation characterised by form of heating method
- F22B1/02—Methods of steam generation characterised by form of heating method by exploitation of the heat content of hot heat carriers
- F22B1/023—Methods of steam generation characterised by form of heating method by exploitation of the heat content of hot heat carriers with heating tubes, for nuclear reactors as far as they are not classified, according to a specified heating fluid, in another group
- F22B1/026—Methods of steam generation characterised by form of heating method by exploitation of the heat content of hot heat carriers with heating tubes, for nuclear reactors as far as they are not classified, according to a specified heating fluid, in another group with vertical tubes between to horizontal tube sheets
-
- G—PHYSICS
- G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
- G21C—NUCLEAR REACTORS
- G21C1/00—Reactor types
- G21C1/32—Integral reactors, i.e. reactors wherein parts functionally associated with the reactor but not essential to the reaction, e.g. heat exchangers, are disposed inside the enclosure with the core
- G21C1/326—Integral reactors, i.e. reactors wherein parts functionally associated with the reactor but not essential to the reaction, e.g. heat exchangers, are disposed inside the enclosure with the core wherein the heat exchanger is disposed next to or beside the core
-
- G—PHYSICS
- G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
- G21C—NUCLEAR REACTORS
- G21C19/00—Arrangements for treating, for handling, or for facilitating the handling of, fuel or other materials which are used within the reactor, e.g. within its pressure vessel
- G21C19/28—Arrangements for introducing fluent material into the reactor core; Arrangements for removing fluent material from the reactor core
-
- G—PHYSICS
- G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
- G21D—NUCLEAR POWER PLANT
- G21D1/00—Details of nuclear power plant
- G21D1/006—Details of nuclear power plant primary side of steam generators
-
- G—PHYSICS
- G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
- G21C—NUCLEAR REACTORS
- G21C1/00—Reactor types
- G21C1/32—Integral reactors, i.e. reactors wherein parts functionally associated with the reactor but not essential to the reaction, e.g. heat exchangers, are disposed inside the enclosure with the core
-
- G21Y2004/30—
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E30/00—Energy generation of nuclear origin
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E30/00—Energy generation of nuclear origin
- Y02E30/30—Nuclear fission reactors
Definitions
- the following relates to the nuclear reactor arts, steam generator and steam generation arts, electrical power generation arts, and related arts.
- Compact nuclear reactors are known for maritime and land-based power generation applications and for other applications.
- an integral steam generator is located inside the reactor pressure vessel, which has advantages such as compactness, reduced likelihood of a severe loss of coolant accident (LOCA) event due to the reduced number and/or size of pressure vessel penetrations, retention of the radioactive primary coolant entirely within the reactor pressure vessel, and so forth.
- LOCA severe loss of coolant accident
- an apparatus comprises: a generally cylindrical pressure vessel defining a cylinder axis; a nuclear reactor core disposed in the generally cylindrical pressure vessel; a central riser disposed coaxially inside the generally cylindrical pressure vessel, the central riser being hollow and having a bottom end proximate to the nuclear reactor core to receive primary coolant heated by the nuclear reactor core, the central riser having a top end distal from the nuclear reactor core; and a once-through steam generator (OTSG) comprising tubes arranged parallel with the cylinder axis in an annular volume defined between the central riser and the generally cylindrical pressure vessel, primary coolant discharged from the top end of the central riser flowing inside the tubes toward the nuclear reactor core, the OTSG further including a fluid flow volume having a feedwater inlet and a steam outlet wherein fluid injected into the fluid flow volume at the feedwater inlet and discharged from the fluid flow volume at the steam outlet flows outside the tubes in a direction generally opposite flow of primary coolant inside the tubes.
- OTSG once-through steam generator
- an apparatus comprises: a pressurized water nuclear reactor (PWR) including a pressure vessel, a nuclear reactor core disposed in the pressure vessel, and a vertically oriented hollow central riser disposed above the nuclear reactor core inside the pressure vessel; and a once-through steam generator (OTSG) disposed in the pressure vessel of the PWR, the OTSG including vertical tubes arranged in at least one of (i) the central riser and (ii) an annular volume defined by the central riser and the pressure vessel, the OTSG further including a fluid flow volume surrounding the vertical tubes; wherein the PWR has an operating state in which feedwater injected into the fluid flow volume at a feedwater inlet is converted to steam by heat emanating from primary coolant flowing inside the tubes of the OTSG, and the steam is discharged from the fluid flow volume at a steam outlet.
- PWR pressurized water nuclear reactor
- OTSG once-through steam generator
- a method comprises: constructing a once-through steam generator (OTSG), the constructing including mounting tubes of the OTSG under axial tension; and operating the OTSG at an elevated temperature at which the tubes are under axial compression.
- OTSG once-through steam generator
- the invention may take form in various components and arrangements of components, and in various process operations and arrangements of process operations.
- the drawings are only for purposes of illustrating preferred embodiments and are not to be construed as limiting the invention.
- FIG. 1 diagrammatically shows a perspective partial-sectional view a nuclear reactor including an integral steam generator as disclosed herein.
- FIG. 2 diagrammatically shows a side sectional view of the upper vessel section of the nuclear reactor of FIG. 1 with the tubes of the steam generator omitted to emphasize the downcomer volume.
- FIG. 3 diagrammatically shows Section D-D indicated in FIG. 2 .
- FIG. 4 diagrammatically shows flow of the primary and secondary coolant fluids in the integral steam generator of FIG. 1 .
- FIG. 5 diagrammatically shows an illustrative process for manufacturing and deploying the integral steam generator of FIG. 1 .
- FIG. 6 diagrammatically illustrates the upper pressure vessel portion of a variant embodiment.
- a nuclear reactor core 10 is disposed inside a generally cylindrical pressure vessel.
- the pressure vessel includes a lower pressure vessel portion or section 12 housing the nuclear reactor core 10 , an upper vessel portion or section 14 , and mid-flange region 16 .
- the pressure vessel 12 , 14 , 16 contains primary coolant, which in the illustrative case of a light water reactor is water (H 2 O), optionally including other additives for reactivity control, such as a boron compound (e.g., “borated water”).
- the primary coolant may be another fluid, such as heavy water (D 2 O).
- the primary coolant fills most or all of the volume of the pressure vessel 12 , 14 , 16 .
- a reactor inlet annulus 18 surrounds the reactor core 10 to enable primary coolant to flow to the reactor core 10 .
- Optional shielding or shrouding 20 disposed in the reactor inlet annulus 18 provides additional radiation shielding from the reactor core 10 .
- the illustrative reactor is a pressurized water reactor (PWR) in which the primary coolant is sub-cooled light water maintained under an elevated pressure at a temperature below the boiling point (saturation temperature) at the operating pressure; however, a boiling water reactor (BWR) in which the primary coolant operates at the saturation temperature at an elevated pressure, or another reactor configuration such as a configuration employing heavy water, is also contemplated.
- PWR pressurized water reactor
- BWR boiling water reactor
- Reactor control is provided by upper internal neutron-absorbing control rods 22 and a control rod drive mechanism (CRDM) 24 that is configured to controllably insert and withdraw the control rods into and out of the nuclear reactor core 10 .
- Diagrammatic FIG. 1 only identifies two illustrative control rods 22 ; however, in some embodiments the control rods may number in the dozens or hundreds, with insertion points spatially distributed across the reactor core area to collectively provide uniform reaction control.
- the CRDM 24 may be divided into multiple units (details not illustrated), each controlling one or more control rods. For example, a plurality of control rods may be operatively coupled with a single CRDM unit via a connecting rod/spider assembly or other suitable coupling (details not illustrated).
- a CRDM unit includes a motor driving a lead screw operatively connected with control rods via a connecting rod/spider assembly, such that motor operation causes linear translation of the assembly including the lead screw, connecting rod, spider, and control rods.
- Such CRDM units provide fine control of the precise insertion of the control rods into the reactor core 10 via the lead screw, and hence are suitable for “gray rod” operation providing fine incremental reaction control.
- a CRDM unit may comprise a lifting piston that lifts an assembly including the connecting rod, spider, and control rods out of the reactor core 10 , and during a SCRAM removes the lifting force to allow the control rods to fall into the reactor core 10 by gravity and optional hydraulic pressure force(s).
- Such CRDM units are suitably used for “shutdown rod” operation, as part of the reactor safety system.
- the gray rod and shutdown rod functionality is integrated into a single CRDM unit, for example using a separable ball nut coupling with a lead screw such that the CRDM unit normally provides gray rod functionality but during a SCRAM the ball nut separates to release the control rods into the reactor core 10 .
- CRDM units providing gray/shutdown rod functionality, in which the connection between the motor and the lead screw is not releasable, but rather a separate latch is provided between the lead screw and the connecting rod in order to effectuate SCRAM.
- the lead screw does not SCRAM, but rather only the unlatched connecting rod and control rod SCRAM together toward the reactor core while the lead screw remains engaged with the motor.
- the diagrammatically illustrated CRDM 24 may include one or more CRDM units including various combinations of CRDM units of the described types or other CRDM unit configurations providing gray and/or shutdown rod functionality.
- the illustrative CRDM 24 is an internal CRDM in which all mechanical and electromagnetomotive components, including the motor, lead screw, connecting rod, and so forth are disposed inside the pressure vessel 12 , 14 , 16 , with only electrical wires, hydraulic lines, or other power or control leads connecting with these components.
- the CRDM may employ external CRDM units in which the motor is mounted outside the pressure vessel, for example above or below.
- the primary coolant may be circulated naturally, due to natural convection set up by heating due of the primary coolant in the vicinity of the operating nuclear reactor core 10 .
- the primary coolant circulation may be driven or assisted by optional reactor coolant pumps 26 .
- the diagrammatically illustrated coolant pumps 26 are internal pumps having rotor and stator elements both located inside the pressure vessel 12 , 14 , 16 .
- an external pump can be employed, for example having an external stator and a rotor coupled with the pressure vessel volume via a suitable conduit or tube, or the circulation pumps may be omitted entirely, as per natural convection reactor embodiments.
- FIG. 2 illustrates a side sectional view of the upper vessel 14 and selected components therein, while FIG. 3 shows Section D-D indicated in FIG. 2 .
- the illustrative nuclear reactor is an integral nuclear reactor, by which it is meant that a steam generator 30 is integrated inside the pressure vessel 12 , 14 , 16 .
- the pressure vessel 12 , 14 , 16 is generally cylindrical and defines a cylinder axis A (labeled only in FIG. 2 ).
- the steam generator 30 is a straight-tube once-through steam generator (OTSG) 30 disposed in the upper vessel 14 .
- OTSG straight-tube once-through steam generator
- the OTSG 30 includes straight tubes 32 arranged vertically in parallel with the cylinder axis A in an annular “downcomer” volume 34 defined between: (i) a hollow central riser 36 disposed coaxially in the upper portion 14 of the generally cylindrical pressure vessel, and (ii) the upper portion 14 of the generally cylindrical pressure vessel.
- the hollow central riser 36 defines a central riser flow path 38 inside the central riser 36 .
- the OTSG 30 also includes an outer shroud 40 surrounding the tubes 32 disposed in the downcomer volume 34 , and an inner shroud 42 disposed between the central riser 36 and the tubes 32 . (Note that in FIGS. 2 and 3 , the OTSG shrouds 40 , 42 are shown and labeled, but the tubes 32 are omitted so as to more clearly show the annular downcomer volume 34 in FIGS. 2 and 3 ).
- the primary coolant flow path in the illustrative reactor is as follows.
- the central riser 36 has a bottom end proximate to the nuclear reactor core 10 to receive primary coolant heated by the nuclear reactor core 10 , and a top end distal from the nuclear reactor core 10 .
- Primary coolant heated by the nuclear reactor core 10 flows upward through the central riser flow path 38 inside the central riser 36 .
- the primary coolant flow turns 180° (that is, from flowing generally upward to flowing generally downward).
- the primary coolant enters the tubes 32 of the OTSG 30 and flows downward through the tubes 32 .
- the primary coolant is discharged from the lower ends of the tubes 32 into a primary outlet plenum 44 , which passes the primary coolant flow back to the reactor inlet annulus 18 and back to the reactor core 10 .
- the outer and inner shrouds 40 , 42 of the OTSG 30 define a fluid flow volume of the OTSG 30 between the shrouds 40 , 42 .
- This fluid flow volume surrounds the tubes 32 , and has a feedwater inlet 50 and a steam outlet 52 .
- a single inlet 50 and single outlet 52 are illustrated, in other embodiments there may be multiple inlets and/or multiple outlets, to provide redundancy and/or improved radial symmetry in the plane transverse to the axis A.
- Fluid e.g., feedwater
- Fluid flow volume e.g., as steam
- feedwater injected into the fluid flow volume of the OTSG 30 at the feedwater inlet 50 is converted to steam by heat emanating from primary coolant flowing inside the tubes 32 of the OTSG 30 , and the steam is discharged from the fluid flow volume at a steam outlet 52 .
- FIG. 4 shows portions of three illustrative tubes 32 carrying downward primary coolant flow (F primary ).
- the fluid flow volume of the OTSG 30 is diagrammatically shown in FIG. 4 by indication of portions of the outer and inner shrouds 40 , 42 that define the fluid flow volume of the OTSG 30 .
- the axial direction corresponding to the axis A of the generally cylindrical pressure vessel is also indicated in FIG. 4 .
- the fluid flowing in the fluid flow volume of the OTSG 30 is sometimes referred to herein as “secondary” coolant, and the generally upward “counter” flow of the secondary coolant in the fluid flow volume of the OTSG 30 is indicated as secondary coolant flow (F secondary ) in diagrammatic FIG. 4 .
- secondary coolant flow F secondary
- the steam flow S secondary is also diagrammatically indicated in FIG. 4 by using dotted arrows).
- the steam flow Ssecondary exiting the steam outlet 52 suitably serves as working steam that flows to and operates a turbine or other steam-operated device.
- the fluid flow volume of the OTSG 30 is defined by the outer and inner shrouds 40 , 42 that are separate from the central riser 36 and the upper portion 14 of the pressure vessel.
- the OTSG 30 to be constructed as a unit including the tubes 32 and surrounding shrouds 40 , 42 , and to then be installed as a unit in the upper portion 14 of the pressure vessel.
- the inner shroud to be embodied as an outer surface of the central riser 36
- the outer shroud to be embodied as an inner surface of the upper portion 14 of the pressure vessel.
- annular space between the outer shroud 40 and the pressure vessel 14 may optionally be employed for a useful purpose.
- the annular space between the outer shroud 40 and the pressure vessel 14 defines a feedwater annulus 60 between an outer shroud 40 of the OTSG 30 and the pressure vessel (upper portion 14 ) buffers feedwater injected into the fluid flow volume at the feedwater inlet 50 .
- a steam annulus 62 between the outer shroud 40 of the OTSG 30 and the pressure vessel (upper portion 14 ) buffers steam discharged from the fluid flow volume at the steam outlet 52 .
- the feedwater annulus and the steam annulus have equal inner diameters and equal outer diameters.
- the outer shroud and the relevant pressure vessel portion have constant diameters over the axial length of the annuluses.
- the feedwater annulus 60 has a larger outer diameter than the steam annulus 62 . This is obtained by increasing the diameter of the upper pressure vessel portion 14 surrounding the feedwater annulus 60 as compared with the diameter of the upper pressure vessel portion 14 surrounding the steam annulus 62 .
- the diameter of the outer shroud 40 remains constant over the axial length of the annuluses 60 , 62 . This configuration allows a larger local inventory of water so that the time available for steam generator boil-off is relatively longer in the event of a loss-of-feedwater (LOFW) accident.
- LOFW loss-of-feedwater
- the flow circuit for the primary coolant includes a 180° flow reversal as the primary coolant discharges from the central riser flow path 38 inside the central riser 36 and flows into the top ends of the tubes 32 of the OTSG 30 .
- a flow diverter 70 is provided to facilitate this flow reversal.
- the illustrative flow diverter 70 is disposed in the generally cylindrical pressure vessel 14 and has a flow diverting surface 72 facing the top end of the central riser that is sloped or (as illustrated) curved to redirect primary coolant discharged from the top end of the central riser 36 toward inlets of the tubes 32 of the OTSG 30 .
- the flow diverter 70 is spaced apart from the top of the central riser 36 by a primary inlet plenum 74 .
- the illustrative nuclear reactor is a pressurized water reactor (PWR) in which the primary coolant is sub-cooled and maintained under positive pressure.
- the pressurization of the primary coolant is provided by an external pressurizer.
- the pressurization of the primary coolant is provided by an internal pressurizer.
- the flow diverter 72 also serves as a part of the divider plate 70 spaced apart from the top end of the central riser 36 by the aforementioned primary inlet plenum 74 .
- the generally cylindrical pressure vessel 12 , 14 , 16 (and, more precisely, the upper pressure vessel portion 14 ) includes a sealing top portion 78 cooperating with the divider plate 70 to define an integral pressurizer volume 80 that is separated by the divider plate 70 from the remaining interior volume of the generally cylindrical pressure vessel 12 , 14 , 16 .
- the integral pressurizer volume 80 contains fluid (saturated primary coolant liquid and steam) at a temperature that is greater than the temperature of the primary coolant disposed in the remaining interior volume of the generally cylindrical pressure vessel 12 , 14 , 16 .
- the saturation temperature is maintained by pressurizer heaters 82 (shown only in FIG.
- pressurizer spray nozzles 84 provide a mechanism for reducing the pressure by condensing some of the steam vapor in volume 80 .
- the divider plate 70 suitably includes openings (not shown) providing hydraulic fluid communication between the integral pressurizer volume 80 and the remaining interior volume of the generally cylindrical pressure vessel 12 , 14 , 16 . This hydraulic fluid communication establishes the pressure level in the remaining interior volume of the generally cylindrical pressure vessel 12 , 14 , 16 . Since there is a temperature difference across divider plate 70 between the pressurizer volume 80 and primary inlet plenum 74 , the remaining primary fluid in the interior volume of the generally cylindrical pressure vessel 12 , 14 , 16 is maintained at sub-cooled liquid conditions at a temperature approximately 11° C.
- the reactor core 10 in the operating state operates at 425 MW thermal.
- the hot reactor coolant water flows in a circuit, called the hot leg, which includes the space above the core flowing around the CRDM's 24 .
- the hot leg extends up the central riser 36 to the inlet plenum 74 , wherein the reactor coolant subsequently enters into the tubes 32 of the straight-tube OTSG 30 via the central riser flow path 38 .
- the straight-tube OTSG 30 encircles the central riser 36 and includes the annular array of steam generator tubes 32 disposed in the annulus between the central riser 36 and the outer shroud 40 of the OTSG 30 .
- the central riser 36 is a high pressure component separating the high pressure reactor primary coolant at 1900 psia (in this illustrative quantitative embodiment) from the lower pressure secondary coolant which in this example is at 825 psia.
- the use of an internal pressure part via the central riser 36 yields a compact and efficient design since the primary pressure boundary is internal to the steam generator 30 and serves the dual use as a riser defining the flow path 38 for the hot leg.
- One design consideration is that there is differential thermal expansion between central riser 36 , the tubes 32 , and the upper vessel 14 . The differential expansion is further complicated by the feedwater annulus 60 containing feedwater at a substantially lower temperature than the steam in the steam annulus 62 , which results in a range of temperatures in the upper vessel 14 , causing additional thermal stress.
- the tubes 32 are made of an austenitic nickel-chromium-based alloy, such as InconelTM 690, and the tubes 32 are secured in a support made of steel.
- the support includes an upper tubesheet 90 and a lower tubesheet 92 (diagrammatically indicated in FIG. 2 )
- the austenitic nickel-chromium-based alloy will have a higher coefficient of thermal expansion than the steel.
- the balancing of the stresses over the operational and non-operational range of conditions is suitably accomplished by pre-stressing the InconelTM 690 steam generator tubes 32 by expanding the tubes 32 into mating holes of the upper and lower tubesheets 90 , 92 .
- This expansion draws the tubes into tension via the Poisson effect.
- the concept is that in the operating state of the nuclear reactor the primary coolant flowing in the tubes 32 of the OTSG 30 is at a relatively high temperature, for example a temperature of at least 500° C., and the tubes 32 of the OTSG 30 are designed to be under axial compression in this operating state at high temperature.
- the tubes 32 of the OTSG 30 are designed to be under axial tension in a non-operating state of the nuclear reactor in which the tubes 32 are at a substantially lower temperature such as room temperature, for example suitably quantified as a temperature of less than 100° C.
- the balancing of the stresses over the operational and non-operational range is achieved by pre-stressing the tubes 32 to be in axial tension at room temperature (e.g., at less than 100° C. in some embodiments), so that the differential thermal expansion between the InconelTM 690 steam generator tubes 32 and the steel of the central riser 36 and vessel 14 causes the tubes to transition from axial tension to axial compression as the temperature is raised to the operating temperature, e.g. at least 500° C. in some embodiments.
- a manufacturing sequence to prestress the tubes 32 to place them into axial tension is further described.
- the tubes 32 are mounted in the tubesheets 90 , 92 of the OTSG frame or support by expanding the tube ends to secure them to the tubesheets 90 , 92 .
- a consequential operation 102 is that this imparts axial tension to the tubes 32 .
- the OTSG 30 including the prestressed tubes 32 is installed in the pressure vessel 12 , 14 , 16 to construct the integral PWR of FIGS. 1-4 .
- the integral PWR is started up and brought to its operating state which has the effect of raising the temperature the primary coolant flowing in the tubes 32 of the OTSG 30 to an operating temperature of (in the illustrative example) at least 500° C.
- a consequential operation 108 is that this imparts axial compression to the tubes 32 due to the relatively higher coefficient of thermal expansion of the austenitic nickel-chromium-based alloy of the tubes 32 as compared with the steel of the central riser 36 and vessel 14 connected via tubesheets 90 , 92 .
- the OTSG 30 defines an integral economizer that heats feedwater injected into the fluid flow volume at the feedwater inlet 50 to a temperature at or below a boiling point of the feedwater.
- the straight-tube OTSG 30 is an integral economizer (IEOTSG) design since the feedwater is heated by flow outside of the tubes 32 .
- Feedwater enters through the feedwater nozzles 50 , distributes throughout the feedwater annulus 60 , and enters the tubes 32 via a gap or other passage (not shown) between the bundle shroud 40 and the lower tubesheet 92 .
- feedwater flows outside of the tubes 32 and there is forced convection heat transfer from the primary coolant flow to the feedwater flow followed by subcooled and saturated boiling to form the steam flow.
- the critical heat flux is reached at approximately 95% steam quality
- the steam goes through a transition to stable film boiling followed by dryout at 100% steam quality.
- the forced convection to steam raises the temperature to superheated conditions at which the steam exits the steam generator via the steam outlet annulus 62 and the steam outlet nozzle 52 .
- the superheated steam does not require moisture separators before the steam is delivered to the steam turbine (although it is contemplated to include moisture separators in some embodiments).
- the pressurizer controls the pressure of the primary coolant via the pressurizer heaters 82 and the pressurizer spray nozzles 84 .
- the heaters 82 are turned on by a reactor control system (not shown).
- the spray nozzles 84 inject cold leg water from the top of the reactor inlet annulus 18 on the discharge side of the reactor coolant pumps 26 via a small external line (not shown).
- the pressurizer volume 80 is formed by a divider plate 70 which separates the space between the primary inlet plenum 74 and the pressurizer volume 80 .
- the divider plate 70 optionally also serves as a flow diverter by including a perforated cylinder 124 ( FIG.
- the illustrative pressurizer including the pressurizer volume 80 and pressure control structures 82 , 84 advantageously is a fully integral pressurizer (that is, is part of the pressure vessel 12 , 14 , 16 ) and advantageously has no pass-throughs for external CRDM's or other components.
- the central riser 36 forms a path 38 for the primary coolant flow leaving the reactor core 10 to reach the primary inlet plenum 74 of the steam generator 30 .
- the reactor is operated in a natural circulation mode with the reactor coolant pumps 26 turned off (as may occur during a malfunction or loss of electrical power causing the pumps 26 to stop operating), the hot rising primary coolant is only impeded by the upper internals (e.g., the CRDM's 24 ).
- This flow resistance is not large compared to the flow resistance of the core 10 and the steam generator tubes 32 because the flow area is relatively large.
- the flow resistance of the central riser 36 is also a relatively small percentage of the total because of the large diameter of the path 38 .
- the straight-tube OTSG 30 with integral pressurizer volume 80 disclosed herein automatically removes non-condensable gases from the primary coolant circulation loop since there is only one high point at the top of the pressurizer volume 80 . Buoyancy causes the non-condensable gases and vapor to go to the top of the pressurizer volume 80 , where these gases and vapor do not interfere with the natural circulation loop.
- LOCA loss of coolant accident
- Another advantage of the disclosed straight-tube OTSG 30 is that it can optionally operate in multiple modes to remove decay heat from the reactor core 10 .
- the reactor coolant pumps 26 stop operating, then the primary coolant water continues to circulate, albeit now via natural circulation, through the core 10 and through the steam generator tubes 32 .
- feedwater supplied to the inlet 50 of the steam generator 30 there is a large tube surface area to remove radioactive fission product heat from the core 10 . If the primary coolant level falls below the level of the primary inlet plenum 74 during a LOCA, then the straight-tube OTSG 30 can operate as a condenser.
- the primary coolant pressure is inside the tubes 32 .
- the primary coolant is at a substantially higher pressure than the secondary coolant flowing through the fluid flow volume defined outside the tubes 32 by the shrouds 40 , 42 .
- the primary coolant flowing inside the tubes 32 is at a pressure that is at least twice a pressure of the secondary fluid (feedwater or steam) in the fluid flow volume. This enables the use of a thinner tube wall in tension.
- the primary coolant flows outside the tubes then the tube is in compression and a thicker tube wall is generally required.
- the use of thinner tube walls translates into the OTSG 30 being substantially lighter and including substantially less InconelTM 690 or other nickel-chromium-based alloy material used for the tubes 32 .
- the weight saving of the straight-tube OTSG 30 is advantageous for an integral nuclear reactor. For example, in the illustrative embodiment of FIGS. 1-3 , during refueling the core 10 is accessed by removing the steam generator 30 . This entails disconnecting the OTSG 30 from the lower pressure vessel portion 12 via the mid-flange 16 .
- the lightweight straight-tube OTSG 30 advantageously reduces the requisite size of the containment structure crane used for lifting the steam generator 30 off to the side during refueling.
- the straight-tube OTSG 30 also has service and maintenance advantages. Manways are readily provided proximate to the pressurizer volume 80 and the primary inlet plenum 74 to provide service access. Inspection of the tubes 32 can be performed during a plant outage via the primary inlet plenum 74 without removing the steam generator 30 from the pressure vessel. Eddy current inspection thusly performed can reveal tube thinning and tube cracks. If tube plugging is indicated by such inspection, the steam generator 30 can be removed during the outage and tube plugs can be installed at the lower tubesheet 92 and the upper tubesheet 90 . In another approach, both tube inspection and tube plugging can be done during refueling when the steam generator 30 is placed off to the side of the reactor. In this case, there is easy access from the bottom for tube inspection and plugging.
- This variant embodiment includes the IEOTSG 30 with tubes 32 mounted in upper and lower tubesheets 90 , 92 .
- a modified upper pressure vessel portion 14 ′ differs from the upper pressure vessel portion 14 in that it does not have a larger diameter to provide a feedwater annulus with larger outer diameter as compared with the steam annulus. Rather, a feedwater annulus 60 ′ connected with the feedwater inlet 50 in the variant embodiment of FIG. 6 is of the same outer diameter as the steam annulus 62 that is connected with the steam outlet 52 .
- the modified upper pressure vessel portion 14 ′ also differs from the upper pressure vessel portion 14 in that it does not include the integral sealing top portion 78 .
- a separate sealing top portion 78 ′ is provided which is secured to the modified upper pressure vessel portion 14 ′ by an upper flange 120 . Still further, the variant embodiment also does not include an integral pressurizer volume or the diverter plate 70 . Rather, the sealing top portion 78 ′ defines a modified primary inlet plenum 74 ′ (but does not define a pressurizer volume), and the sealing top portion 78 ′ includes a curved surface 122 that cooperates with cylinder openings 124 at the top of the central riser 36 to perform the primary coolant flow diversion functionality.
- primary coolant pressurization for the embodiment of FIG. 6 is suitably provided by self-pressurization.
- steam vapor from the reactor core collects at the top of the steam generator vessel, that is, in the primary inlet plenum 74 ′.
- the compressibility of the vapor filled dome volume 74 ′ regulates the primary coolant pressure.
- the feedwater flow into the feedwater inlet 50 is increased which increases the boiling lengths in the tubes 32 .
- the reactor core 10 follows the load demand by increasing power via a negative moderator coefficient of reactivity due to the reduction in core inlet temperature from the steam generator 30 .
- the core outlet temperature is maintained at a near constant temperature regulated by the pressure and saturation temperature of the steam dome volume 74 ′. Accordingly, for an increase in power, the temperature rise across the reactor core 10 increases while the reactor flow rate remains constant as determined by the reactor coolant pumps 26 . Decreasing power employs analogous processes.
- the tubes of the OTSG can be placed in different locations within the pressure vessel.
- the OTSG 30 including tubes 32 is disposed entirely in the downcomer volume 34 . More generally, however, tubes may be disposed in the downcomer volume (as illustrated), or in the central riser flow path 38 inside the central riser 36 , or in both volumes 34 , 36 .
- the separate inner shroud 42 may instead be embodied as an outer surface of the central riser 36 , and/or for the separate outer shroud 40 may instead be embodied as an inner surface of the upper portion 14 of the pressure vessel. Additionally, it is contemplated to integrate the lower tubesheet 92 with the mid-flange 16 .
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Abstract
Description
- This application is a continuation of U.S. patent application Ser. No. 12/891,317, filed Sep. 27, 2010, now U.S. Pat. No. 9,343,187, the entire disclosure of which is incorporated by reference herein.
- The following relates to the nuclear reactor arts, steam generator and steam generation arts, electrical power generation arts, and related arts.
- Compact nuclear reactors are known for maritime and land-based power generation applications and for other applications. In some such nuclear reactors, an integral steam generator is located inside the reactor pressure vessel, which has advantages such as compactness, reduced likelihood of a severe loss of coolant accident (LOCA) event due to the reduced number and/or size of pressure vessel penetrations, retention of the radioactive primary coolant entirely within the reactor pressure vessel, and so forth.
- Disclosed herein are further improvements that provide reduced cost, simplified manufacturing, and other benefits that will become apparent to the skilled artisan upon reading the following.
- In one aspect of the disclosure, an apparatus comprises: a generally cylindrical pressure vessel defining a cylinder axis; a nuclear reactor core disposed in the generally cylindrical pressure vessel; a central riser disposed coaxially inside the generally cylindrical pressure vessel, the central riser being hollow and having a bottom end proximate to the nuclear reactor core to receive primary coolant heated by the nuclear reactor core, the central riser having a top end distal from the nuclear reactor core; and a once-through steam generator (OTSG) comprising tubes arranged parallel with the cylinder axis in an annular volume defined between the central riser and the generally cylindrical pressure vessel, primary coolant discharged from the top end of the central riser flowing inside the tubes toward the nuclear reactor core, the OTSG further including a fluid flow volume having a feedwater inlet and a steam outlet wherein fluid injected into the fluid flow volume at the feedwater inlet and discharged from the fluid flow volume at the steam outlet flows outside the tubes in a direction generally opposite flow of primary coolant inside the tubes.
- In another aspect of the disclosure, an apparatus comprises: a pressurized water nuclear reactor (PWR) including a pressure vessel, a nuclear reactor core disposed in the pressure vessel, and a vertically oriented hollow central riser disposed above the nuclear reactor core inside the pressure vessel; and a once-through steam generator (OTSG) disposed in the pressure vessel of the PWR, the OTSG including vertical tubes arranged in at least one of (i) the central riser and (ii) an annular volume defined by the central riser and the pressure vessel, the OTSG further including a fluid flow volume surrounding the vertical tubes; wherein the PWR has an operating state in which feedwater injected into the fluid flow volume at a feedwater inlet is converted to steam by heat emanating from primary coolant flowing inside the tubes of the OTSG, and the steam is discharged from the fluid flow volume at a steam outlet.
- In another aspect of the disclosure, a method comprises: constructing a once-through steam generator (OTSG), the constructing including mounting tubes of the OTSG under axial tension; and operating the OTSG at an elevated temperature at which the tubes are under axial compression.
- The invention may take form in various components and arrangements of components, and in various process operations and arrangements of process operations. The drawings are only for purposes of illustrating preferred embodiments and are not to be construed as limiting the invention.
-
FIG. 1 diagrammatically shows a perspective partial-sectional view a nuclear reactor including an integral steam generator as disclosed herein. -
FIG. 2 diagrammatically shows a side sectional view of the upper vessel section of the nuclear reactor ofFIG. 1 with the tubes of the steam generator omitted to emphasize the downcomer volume. -
FIG. 3 diagrammatically shows Section D-D indicated inFIG. 2 . -
FIG. 4 diagrammatically shows flow of the primary and secondary coolant fluids in the integral steam generator ofFIG. 1 . -
FIG. 5 diagrammatically shows an illustrative process for manufacturing and deploying the integral steam generator ofFIG. 1 . -
FIG. 6 diagrammatically illustrates the upper pressure vessel portion of a variant embodiment. - With reference to
FIG. 1 , a perspective partial-sectional view an illustrative nuclear reactor is shown. Anuclear reactor core 10 is disposed inside a generally cylindrical pressure vessel. In the illustrative embodiment the pressure vessel includes a lower pressure vessel portion orsection 12 housing thenuclear reactor core 10, an upper vessel portion orsection 14, andmid-flange region 16. This is merely an illustrative configuration, and the pressure vessel can in general be constructed of as few as a single portion or section, or two portions or sections, three portions or sections (as illustrated), four portions or sections (for example including a fourth upper “cap” portion or section separate from the upper portion or section), or so forth. Thepressure vessel pressure vessel reactor inlet annulus 18 surrounds thereactor core 10 to enable primary coolant to flow to thereactor core 10. Optional shielding or shrouding 20 disposed in thereactor inlet annulus 18 provides additional radiation shielding from thereactor core 10. The illustrative reactor is a pressurized water reactor (PWR) in which the primary coolant is sub-cooled light water maintained under an elevated pressure at a temperature below the boiling point (saturation temperature) at the operating pressure; however, a boiling water reactor (BWR) in which the primary coolant operates at the saturation temperature at an elevated pressure, or another reactor configuration such as a configuration employing heavy water, is also contemplated. - Reactor control is provided by upper internal neutron-absorbing
control rods 22 and a control rod drive mechanism (CRDM) 24 that is configured to controllably insert and withdraw the control rods into and out of thenuclear reactor core 10. DiagrammaticFIG. 1 only identifies twoillustrative control rods 22; however, in some embodiments the control rods may number in the dozens or hundreds, with insertion points spatially distributed across the reactor core area to collectively provide uniform reaction control. TheCRDM 24 may be divided into multiple units (details not illustrated), each controlling one or more control rods. For example, a plurality of control rods may be operatively coupled with a single CRDM unit via a connecting rod/spider assembly or other suitable coupling (details not illustrated). In some illustrative embodiments, a CRDM unit includes a motor driving a lead screw operatively connected with control rods via a connecting rod/spider assembly, such that motor operation causes linear translation of the assembly including the lead screw, connecting rod, spider, and control rods. Such CRDM units provide fine control of the precise insertion of the control rods into thereactor core 10 via the lead screw, and hence are suitable for “gray rod” operation providing fine incremental reaction control. In some illustrative embodiments, a CRDM unit may comprise a lifting piston that lifts an assembly including the connecting rod, spider, and control rods out of thereactor core 10, and during a SCRAM removes the lifting force to allow the control rods to fall into thereactor core 10 by gravity and optional hydraulic pressure force(s). Such CRDM units are suitably used for “shutdown rod” operation, as part of the reactor safety system. In yet other illustrative embodiments, the gray rod and shutdown rod functionality is integrated into a single CRDM unit, for example using a separable ball nut coupling with a lead screw such that the CRDM unit normally provides gray rod functionality but during a SCRAM the ball nut separates to release the control rods into thereactor core 10. Some further illustrative embodiments of CRDM units are set forth in application Ser. No. 12/722,662 titled “Control Rod Drive Mechanism for Nuclear Reactor” filed Mar. 12, 2010 and related application Ser. No. 12/722,696 titled “Control Rod Drive Mechanism For Nuclear Reactor” filed Mar. 12, 2010 are both incorporated herein by reference in their entireties. These applications disclose CRDM units providing gray/shutdown rod functionality, in which the connection between the motor and the lead screw is not releasable, but rather a separate latch is provided between the lead screw and the connecting rod in order to effectuate SCRAM. In these alternative configurations the lead screw does not SCRAM, but rather only the unlatched connecting rod and control rod SCRAM together toward the reactor core while the lead screw remains engaged with the motor. - The diagrammatically illustrated
CRDM 24 may include one or more CRDM units including various combinations of CRDM units of the described types or other CRDM unit configurations providing gray and/or shutdown rod functionality. Theillustrative CRDM 24 is an internal CRDM in which all mechanical and electromagnetomotive components, including the motor, lead screw, connecting rod, and so forth are disposed inside thepressure vessel - With continuing reference to
FIG. 1 , the primary coolant may be circulated naturally, due to natural convection set up by heating due of the primary coolant in the vicinity of the operatingnuclear reactor core 10. Additionally or alternatively, the primary coolant circulation may be driven or assisted by optional reactor coolant pumps 26. The diagrammatically illustrated coolant pumps 26 are internal pumps having rotor and stator elements both located inside thepressure vessel - The nuclear reactor is further described with continuing reference to
FIG. 1 and with further reference toFIGS. 2 and 3 .FIG. 2 illustrates a side sectional view of theupper vessel 14 and selected components therein, whileFIG. 3 shows Section D-D indicated inFIG. 2 . As seen inFIG. 1 , the illustrative nuclear reactor is an integral nuclear reactor, by which it is meant that asteam generator 30 is integrated inside thepressure vessel pressure vessel FIG. 2 ). Thesteam generator 30 is a straight-tube once-through steam generator (OTSG) 30 disposed in theupper vessel 14. TheOTSG 30 includesstraight tubes 32 arranged vertically in parallel with the cylinder axis A in an annular “downcomer”volume 34 defined between: (i) a hollowcentral riser 36 disposed coaxially in theupper portion 14 of the generally cylindrical pressure vessel, and (ii) theupper portion 14 of the generally cylindrical pressure vessel. The hollowcentral riser 36 defines a centralriser flow path 38 inside thecentral riser 36. The OTSG 30 also includes anouter shroud 40 surrounding thetubes 32 disposed in thedowncomer volume 34, and aninner shroud 42 disposed between thecentral riser 36 and thetubes 32. (Note that inFIGS. 2 and 3 , the OTSGshrouds tubes 32 are omitted so as to more clearly show theannular downcomer volume 34 inFIGS. 2 and 3 ). - The primary coolant flow path in the illustrative reactor is as follows. The
central riser 36 has a bottom end proximate to thenuclear reactor core 10 to receive primary coolant heated by thenuclear reactor core 10, and a top end distal from thenuclear reactor core 10. Primary coolant heated by thenuclear reactor core 10 flows upward through the centralriser flow path 38 inside thecentral riser 36. At the top of thecentral riser 36 the primary coolant flow turns 180° (that is, from flowing generally upward to flowing generally downward). The primary coolant enters thetubes 32 of theOTSG 30 and flows downward through thetubes 32. The primary coolant is discharged from the lower ends of thetubes 32 into aprimary outlet plenum 44, which passes the primary coolant flow back to thereactor inlet annulus 18 and back to thereactor core 10. - With continuing reference to
FIGS. 1-3 and with further reference toFIG. 4 , the outer andinner shrouds OTSG 30 define a fluid flow volume of theOTSG 30 between theshrouds tubes 32, and has afeedwater inlet 50 and asteam outlet 52. Note that although asingle inlet 50 andsingle outlet 52 are illustrated, in other embodiments there may be multiple inlets and/or multiple outlets, to provide redundancy and/or improved radial symmetry in the plane transverse to the axis A. Fluid (e.g., feedwater) is injected into the fluid flow volume at thefeedwater inlet 50 and is discharged from the fluid flow volume (e.g., as steam) at thesteam outlet 52. While in the fluid flow volume, the fluid flows outside thetubes 32 of theOTSG 30 in a generally upward direction generally opposite flow of primary coolant inside thetubes 32. - With continuing reference to
FIGS. 1-3 and with further reference toFIG. 4 , in the operating state of the illustrative PWR, feedwater injected into the fluid flow volume of theOTSG 30 at thefeedwater inlet 50 is converted to steam by heat emanating from primary coolant flowing inside thetubes 32 of theOTSG 30, and the steam is discharged from the fluid flow volume at asteam outlet 52. This is diagrammatically shown inFIG. 4 , which shows portions of threeillustrative tubes 32 carrying downward primary coolant flow (Fprimary). The fluid flow volume of theOTSG 30 is diagrammatically shown inFIG. 4 by indication of portions of the outer andinner shrouds OTSG 30. To facilitate correlation withFIGS. 1-3 , the axial direction corresponding to the axis A of the generally cylindrical pressure vessel is also indicated inFIG. 4 . The fluid flowing in the fluid flow volume of theOTSG 30 is sometimes referred to herein as “secondary” coolant, and the generally upward “counter” flow of the secondary coolant in the fluid flow volume of theOTSG 30 is indicated as secondary coolant flow (Fsecondary) in diagrammaticFIG. 4 . During the upward flow, heat emanating from the primary coolant flow Fprimary transfers to the secondary coolant flow Fsecondary, causing the secondary coolant to heat until it is converted to secondary coolant flow having the form of steam flow (Ssecondary). (The steam flow Ssecondary is also diagrammatically indicated inFIG. 4 by using dotted arrows). Although not illustrated, the steam flow Ssecondary exiting thesteam outlet 52 suitably serves as working steam that flows to and operates a turbine or other steam-operated device. - In the illustrative embodiment, the fluid flow volume of the
OTSG 30 is defined by the outer andinner shrouds central riser 36 and theupper portion 14 of the pressure vessel. Advantageously, this enables theOTSG 30 to be constructed as a unit including thetubes 32 and surroundingshrouds upper portion 14 of the pressure vessel. However, it is also contemplated for the inner shroud to be embodied as an outer surface of thecentral riser 36, and/or for the outer shroud to be embodied as an inner surface of theupper portion 14 of the pressure vessel. - In embodiments which include the
outer shroud 40 which is separate from the upper pressure vessel portion 14 (as in the illustrative embodiment), an annular space between theouter shroud 40 and thepressure vessel 14 may optionally be employed for a useful purpose. In the illustrative example, the annular space between theouter shroud 40 and thepressure vessel 14 defines afeedwater annulus 60 between anouter shroud 40 of theOTSG 30 and the pressure vessel (upper portion 14) buffers feedwater injected into the fluid flow volume at thefeedwater inlet 50. Similarly, asteam annulus 62 between theouter shroud 40 of theOTSG 30 and the pressure vessel (upper portion 14) buffers steam discharged from the fluid flow volume at thesteam outlet 52. - In some embodiments, the feedwater annulus and the steam annulus have equal inner diameters and equal outer diameters. In such embodiments the outer shroud and the relevant pressure vessel portion have constant diameters over the axial length of the annuluses. In the illustrative embodiment, however, the
feedwater annulus 60 has a larger outer diameter than thesteam annulus 62. This is obtained by increasing the diameter of the upperpressure vessel portion 14 surrounding thefeedwater annulus 60 as compared with the diameter of the upperpressure vessel portion 14 surrounding thesteam annulus 62. In the illustrative embodiment the diameter of theouter shroud 40 remains constant over the axial length of theannuluses - With reference to
FIGS. 1 and 2 , as already mentioned the flow circuit for the primary coolant includes a 180° flow reversal as the primary coolant discharges from the centralriser flow path 38 inside thecentral riser 36 and flows into the top ends of thetubes 32 of theOTSG 30. Optionally, aflow diverter 70 is provided to facilitate this flow reversal. Theillustrative flow diverter 70 is disposed in the generallycylindrical pressure vessel 14 and has aflow diverting surface 72 facing the top end of the central riser that is sloped or (as illustrated) curved to redirect primary coolant discharged from the top end of thecentral riser 36 toward inlets of thetubes 32 of the OTSG 30.Theflow diverter 70 is spaced apart from the top of thecentral riser 36 by aprimary inlet plenum 74. - As previously mentioned, the illustrative nuclear reactor is a pressurized water reactor (PWR) in which the primary coolant is sub-cooled and maintained under positive pressure. In some embodiments, the pressurization of the primary coolant is provided by an external pressurizer. However, in the illustrative embodiment the pressurization of the primary coolant is provided by an internal pressurizer. In this configuration, the
flow diverter 72 also serves as a part of thedivider plate 70 spaced apart from the top end of thecentral riser 36 by the aforementionedprimary inlet plenum 74. The generallycylindrical pressure vessel top portion 78 cooperating with thedivider plate 70 to define anintegral pressurizer volume 80 that is separated by thedivider plate 70 from the remaining interior volume of the generallycylindrical pressure vessel integral pressurizer volume 80 contains fluid (saturated primary coolant liquid and steam) at a temperature that is greater than the temperature of the primary coolant disposed in the remaining interior volume of the generallycylindrical pressure vessel FIG. 1 ), whilepressurizer spray nozzles 84 provide a mechanism for reducing the pressure by condensing some of the steam vapor involume 80. Thedivider plate 70 suitably includes openings (not shown) providing hydraulic fluid communication between theintegral pressurizer volume 80 and the remaining interior volume of the generallycylindrical pressure vessel cylindrical pressure vessel divider plate 70 between thepressurizer volume 80 andprimary inlet plenum 74, the remaining primary fluid in the interior volume of the generallycylindrical pressure vessel pressurizer volume 80. This level of sub-cooled liquid prevents the primary fluid inreactor core 10 from experiencing saturated bulk boiling which has a significantly higher vapor volume fraction than sub-cooled nucleate boiling typically present in pressurized water nuclear reactor cores. This prevention of bulk boiling in a PWR core is made possible by the pressurizer (80, 82, 84, 78, and 70) and is beneficial for the integrity of the nuclear reactor fuel rods by minimizing the probability of departure from nucleate boiling (DNB) which increases the fuel pellet and fuel cladding temperatures. - Having set forth an illustrative integral PWR as an illustrative example in
FIGS. 1-4 , some further additional aspects and variants are set forth next. - In one illustrative quantitative example, the
reactor core 10 in the operating state operates at 425 MW thermal. The hot reactor coolant water flows in a circuit, called the hot leg, which includes the space above the core flowing around the CRDM's 24. The hot leg extends up thecentral riser 36 to theinlet plenum 74, wherein the reactor coolant subsequently enters into thetubes 32 of the straight-tube OTSG 30 via the centralriser flow path 38. The straight-tube OTSG 30 encircles thecentral riser 36 and includes the annular array ofsteam generator tubes 32 disposed in the annulus between thecentral riser 36 and theouter shroud 40 of theOTSG 30. An advantage of this configuration is that thecentral riser 36 is a high pressure component separating the high pressure reactor primary coolant at 1900 psia (in this illustrative quantitative embodiment) from the lower pressure secondary coolant which in this example is at 825 psia. The use of an internal pressure part via thecentral riser 36 yields a compact and efficient design since the primary pressure boundary is internal to thesteam generator 30 and serves the dual use as a riser defining theflow path 38 for the hot leg. One design consideration is that there is differential thermal expansion betweencentral riser 36, thetubes 32, and theupper vessel 14. The differential expansion is further complicated by thefeedwater annulus 60 containing feedwater at a substantially lower temperature than the steam in thesteam annulus 62, which results in a range of temperatures in theupper vessel 14, causing additional thermal stress. - One approach for mitigating the effect of these differential stresses is to balance the stresses over the operational and non-operational range of conditions of the steam generator. In one illustrative example, the
tubes 32 are made of an austenitic nickel-chromium-based alloy, such as Inconel™ 690, and thetubes 32 are secured in a support made of steel. The support includes anupper tubesheet 90 and a lower tubesheet 92 (diagrammatically indicated inFIG. 2 ) In general, the austenitic nickel-chromium-based alloy will have a higher coefficient of thermal expansion than the steel. The balancing of the stresses over the operational and non-operational range of conditions is suitably accomplished by pre-stressing the Inconel™ 690steam generator tubes 32 by expanding thetubes 32 into mating holes of the upper andlower tubesheets tubes 32 of theOTSG 30 is at a relatively high temperature, for example a temperature of at least 500° C., and thetubes 32 of theOTSG 30 are designed to be under axial compression in this operating state at high temperature. On the other hand, thetubes 32 of theOTSG 30 are designed to be under axial tension in a non-operating state of the nuclear reactor in which thetubes 32 are at a substantially lower temperature such as room temperature, for example suitably quantified as a temperature of less than 100° C. The balancing of the stresses over the operational and non-operational range is achieved by pre-stressing thetubes 32 to be in axial tension at room temperature (e.g., at less than 100° C. in some embodiments), so that the differential thermal expansion between the Inconel™ 690steam generator tubes 32 and the steel of thecentral riser 36 andvessel 14 causes the tubes to transition from axial tension to axial compression as the temperature is raised to the operating temperature, e.g. at least 500° C. in some embodiments. These differential thermal stresses amongcomponents feedwater nozzle 50 positioned low in the pressure vessel leaving a longersteam outlet annulus 62 to blanket the vessel with high temperature outlet steam, and by reducing axial length of thefeedwater annulus 60 by employing a larger radius for thefeedwater annulus 60. - With brief reference to
FIG. 5 , a manufacturing sequence to prestress thetubes 32 to place them into axial tension is further described. In anoperation 100, thetubes 32 are mounted in thetubesheets tubesheets consequential operation 102 is that this imparts axial tension to thetubes 32. In anoperation 104, theOTSG 30 including theprestressed tubes 32 is installed in thepressure vessel FIGS. 1-4 . In anoperation 106, the integral PWR is started up and brought to its operating state which has the effect of raising the temperature the primary coolant flowing in thetubes 32 of theOTSG 30 to an operating temperature of (in the illustrative example) at least 500° C. Aconsequential operation 108 is that this imparts axial compression to thetubes 32 due to the relatively higher coefficient of thermal expansion of the austenitic nickel-chromium-based alloy of thetubes 32 as compared with the steel of thecentral riser 36 andvessel 14 connected viatubesheets - In some embodiments, in the operating state the
OTSG 30 defines an integral economizer that heats feedwater injected into the fluid flow volume at thefeedwater inlet 50 to a temperature at or below a boiling point of the feedwater. In such embodiments, the straight-tube OTSG 30 is an integral economizer (IEOTSG) design since the feedwater is heated by flow outside of thetubes 32. Feedwater enters through thefeedwater nozzles 50, distributes throughout thefeedwater annulus 60, and enters thetubes 32 via a gap or other passage (not shown) between thebundle shroud 40 and thelower tubesheet 92. In the operating mode, feedwater flows outside of thetubes 32 and there is forced convection heat transfer from the primary coolant flow to the feedwater flow followed by subcooled and saturated boiling to form the steam flow. Once the critical heat flux is reached at approximately 95% steam quality, the steam goes through a transition to stable film boiling followed by dryout at 100% steam quality. Thereafter in the tube bundle, the forced convection to steam raises the temperature to superheated conditions at which the steam exits the steam generator via thesteam outlet annulus 62 and thesteam outlet nozzle 52. The superheated steam does not require moisture separators before the steam is delivered to the steam turbine (although it is contemplated to include moisture separators in some embodiments). - Some further aspects of the integral pressurizer are next described. The pressurizer controls the pressure of the primary coolant via the
pressurizer heaters 82 and thepressurizer spray nozzles 84. To increase system pressure, theheaters 82 are turned on by a reactor control system (not shown). To decrease pressure, thespray nozzles 84 inject cold leg water from the top of thereactor inlet annulus 18 on the discharge side of the reactor coolant pumps 26 via a small external line (not shown). Thepressurizer volume 80 is formed by adivider plate 70 which separates the space between theprimary inlet plenum 74 and thepressurizer volume 80. Thedivider plate 70 optionally also serves as a flow diverter by including a perforated cylinder 124 (FIG. 6 , top of divider plate not shown) or a cone shaped flow diverter surface 72 (FIG. 2 ) or other curved or slanted surface which aids in the turning of the flow in the primary coolant in theinlet plenum 74 before it enters the upper ends of thetubes 32 of theOTSG 30 setting up downward flow inside thetubes 30. The illustrative pressurizer including thepressurizer volume 80 andpressure control structures pressure vessel - The
central riser 36 forms apath 38 for the primary coolant flow leaving thereactor core 10 to reach theprimary inlet plenum 74 of thesteam generator 30. In this embodiment there is no horizontal run of piping for this purpose. As a result, if the reactor is operated in a natural circulation mode with the reactor coolant pumps 26 turned off (as may occur during a malfunction or loss of electrical power causing thepumps 26 to stop operating), the hot rising primary coolant is only impeded by the upper internals (e.g., the CRDM's 24). This flow resistance is not large compared to the flow resistance of thecore 10 and thesteam generator tubes 32 because the flow area is relatively large. The flow resistance of thecentral riser 36 is also a relatively small percentage of the total because of the large diameter of thepath 38. - In some existing nuclear steam supply systems, after a loss of coolant accident (LOCA) steam and non-condensable gases can collect at the high points of the reactor coolant pipes, and can inhibit the natural circulation loop between the reactor core and the steam generators. Advantageously, the straight-
tube OTSG 30 withintegral pressurizer volume 80 disclosed herein automatically removes non-condensable gases from the primary coolant circulation loop since there is only one high point at the top of thepressurizer volume 80. Buoyancy causes the non-condensable gases and vapor to go to the top of thepressurizer volume 80, where these gases and vapor do not interfere with the natural circulation loop. - Another advantage of the disclosed straight-
tube OTSG 30 is that it can optionally operate in multiple modes to remove decay heat from thereactor core 10. Starting with the normal operating state, if the reactor coolant pumps 26 stop operating, then the primary coolant water continues to circulate, albeit now via natural circulation, through thecore 10 and through thesteam generator tubes 32. As long as there is feedwater supplied to theinlet 50 of thesteam generator 30, there is a large tube surface area to remove radioactive fission product heat from thecore 10. If the primary coolant level falls below the level of theprimary inlet plenum 74 during a LOCA, then the straight-tube OTSG 30 can operate as a condenser. In this mode, steam from boiling water in thereactor core 10 rises to fill theprimary inlet plenum 74 and thepressurizer volume 80. The lower temperature water and steam on the secondary side (that is, in the fluid flow volume defined outside thetubes 32 by theshrouds 40, 42) causes condensation inside thesteam generator tubes 30. By gravity alone, the condensate flows out of thesteam generator tubes 32 into theprimary outlet plenum 44 where it is returned to thecore 10. - In the straight-
tube OTSG 30, the primary coolant pressure is inside thetubes 32. The primary coolant is at a substantially higher pressure than the secondary coolant flowing through the fluid flow volume defined outside thetubes 32 by theshrouds tubes 32 is at a pressure that is at least twice a pressure of the secondary fluid (feedwater or steam) in the fluid flow volume. This enables the use of a thinner tube wall in tension. In contrast, if the primary coolant flows outside the tubes then the tube is in compression and a thicker tube wall is generally required. Some analyses have indicated that the tube wall in the tension design of the present OTSG embodiments can be made about one-half as thick as the tube wall thickness required for tubes placed in compression (for comparable tube diameter). - The use of thinner tube walls translates into the
OTSG 30 being substantially lighter and including substantially less Inconel™ 690 or other nickel-chromium-based alloy material used for thetubes 32. The weight saving of the straight-tube OTSG 30 is advantageous for an integral nuclear reactor. For example, in the illustrative embodiment ofFIGS. 1-3 , during refueling thecore 10 is accessed by removing thesteam generator 30. This entails disconnecting theOTSG 30 from the lowerpressure vessel portion 12 via the mid-flange 16. The lightweight straight-tube OTSG 30 advantageously reduces the requisite size of the containment structure crane used for lifting thesteam generator 30 off to the side during refueling. - The straight-
tube OTSG 30 also has service and maintenance advantages. Manways are readily provided proximate to thepressurizer volume 80 and theprimary inlet plenum 74 to provide service access. Inspection of thetubes 32 can be performed during a plant outage via theprimary inlet plenum 74 without removing thesteam generator 30 from the pressure vessel. Eddy current inspection thusly performed can reveal tube thinning and tube cracks. If tube plugging is indicated by such inspection, thesteam generator 30 can be removed during the outage and tube plugs can be installed at thelower tubesheet 92 and theupper tubesheet 90. In another approach, both tube inspection and tube plugging can be done during refueling when thesteam generator 30 is placed off to the side of the reactor. In this case, there is easy access from the bottom for tube inspection and plugging. - With reference to
FIG. 6 , a variant embodiment is described. This variant embodiment includes theIEOTSG 30 withtubes 32 mounted in upper andlower tubesheets pressure vessel portion 14′ differs from the upperpressure vessel portion 14 in that it does not have a larger diameter to provide a feedwater annulus with larger outer diameter as compared with the steam annulus. Rather, afeedwater annulus 60′ connected with thefeedwater inlet 50 in the variant embodiment ofFIG. 6 is of the same outer diameter as thesteam annulus 62 that is connected with thesteam outlet 52. The modified upperpressure vessel portion 14′ also differs from the upperpressure vessel portion 14 in that it does not include the integral sealingtop portion 78. Rather, a separate sealingtop portion 78′ is provided which is secured to the modified upperpressure vessel portion 14′ by anupper flange 120. Still further, the variant embodiment also does not include an integral pressurizer volume or thediverter plate 70. Rather, the sealingtop portion 78′ defines a modifiedprimary inlet plenum 74′ (but does not define a pressurizer volume), and the sealingtop portion 78′ includes acurved surface 122 that cooperates withcylinder openings 124 at the top of thecentral riser 36 to perform the primary coolant flow diversion functionality. - As the
pressurizer volume 80 of the embodiment ofFIGS. 1-3 is omitted in the variant embodiment ofFIG. 6 , primary coolant pressurization for the embodiment ofFIG. 6 is suitably provided by self-pressurization. In this approach, steam vapor from the reactor core collects at the top of the steam generator vessel, that is, in theprimary inlet plenum 74′. The compressibility of the vapor filleddome volume 74′ regulates the primary coolant pressure. To increase power, the feedwater flow into thefeedwater inlet 50 is increased which increases the boiling lengths in thetubes 32. Thereactor core 10 follows the load demand by increasing power via a negative moderator coefficient of reactivity due to the reduction in core inlet temperature from thesteam generator 30. The core outlet temperature is maintained at a near constant temperature regulated by the pressure and saturation temperature of thesteam dome volume 74′. Accordingly, for an increase in power, the temperature rise across thereactor core 10 increases while the reactor flow rate remains constant as determined by the reactor coolant pumps 26. Decreasing power employs analogous processes. - As another illustrative variation (not shown), the tubes of the OTSG can be placed in different locations within the pressure vessel. In the illustrative embodiments of
FIGS. 1-3 and 6 , theOTSG 30 includingtubes 32 is disposed entirely in thedowncomer volume 34. More generally, however, tubes may be disposed in the downcomer volume (as illustrated), or in the centralriser flow path 38 inside thecentral riser 36, or in bothvolumes - As other illustrative variations, it has already been noted that the separate
inner shroud 42 may instead be embodied as an outer surface of thecentral riser 36, and/or for the separateouter shroud 40 may instead be embodied as an inner surface of theupper portion 14 of the pressure vessel. Additionally, it is contemplated to integrate thelower tubesheet 92 with the mid-flange 16. - The preferred embodiments have been illustrated and described. Obviously, modifications and alterations will occur to others upon reading and understanding the preceding detailed description. It is intended that the invention be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.
Claims (15)
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US15/156,114 US10803997B2 (en) | 2010-09-27 | 2016-05-16 | Compact nuclear reactor with integral steam generator |
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US12/891,317 US9343187B2 (en) | 2010-09-27 | 2010-09-27 | Compact nuclear reactor with integral steam generator |
US15/156,114 US10803997B2 (en) | 2010-09-27 | 2016-05-16 | Compact nuclear reactor with integral steam generator |
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US12/891,317 Continuation US9343187B2 (en) | 2010-09-27 | 2010-09-27 | Compact nuclear reactor with integral steam generator |
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US10803997B2 US10803997B2 (en) | 2020-10-13 |
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US12/891,317 Active 2034-01-04 US9343187B2 (en) | 2010-09-27 | 2010-09-27 | Compact nuclear reactor with integral steam generator |
US15/156,114 Active 2033-05-14 US10803997B2 (en) | 2010-09-27 | 2016-05-16 | Compact nuclear reactor with integral steam generator |
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US12/891,317 Active 2034-01-04 US9343187B2 (en) | 2010-09-27 | 2010-09-27 | Compact nuclear reactor with integral steam generator |
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US (2) | US9343187B2 (en) |
EP (1) | EP2622606A1 (en) |
JP (1) | JP2014510897A (en) |
KR (1) | KR20130118862A (en) |
CN (2) | CN102822902B (en) |
AR (1) | AR083109A1 (en) |
CA (1) | CA2808425C (en) |
RU (1) | RU2013106699A (en) |
TW (1) | TWI549138B (en) |
WO (1) | WO2012047438A1 (en) |
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-
2010
- 2010-09-27 US US12/891,317 patent/US9343187B2/en active Active
-
2011
- 2011-09-08 EP EP11831147.1A patent/EP2622606A1/en not_active Withdrawn
- 2011-09-08 WO PCT/US2011/050741 patent/WO2012047438A1/en active Application Filing
- 2011-09-08 KR KR1020137006207A patent/KR20130118862A/en not_active Application Discontinuation
- 2011-09-08 JP JP2013531614A patent/JP2014510897A/en active Pending
- 2011-09-08 CN CN201180004814.7A patent/CN102822902B/en not_active Expired - Fee Related
- 2011-09-08 RU RU2013106699/07A patent/RU2013106699A/en not_active Application Discontinuation
- 2011-09-08 CN CN201610530498.1A patent/CN106205746A/en active Pending
- 2011-09-08 CA CA2808425A patent/CA2808425C/en active Active
- 2011-09-26 AR ARP110103512A patent/AR083109A1/en unknown
- 2011-09-26 TW TW100134639A patent/TWI549138B/en active
-
2016
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Cited By (7)
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US11120920B2 (en) * | 2013-10-24 | 2021-09-14 | Smr Inventec, Llc | Steam generator for nuclear steam supply system |
US11798694B2 (en) | 2015-09-30 | 2023-10-24 | Terrapower, Llc | Molten fuel nuclear reactor |
US10902960B2 (en) * | 2018-02-02 | 2021-01-26 | Bwxt Canada Ltd. | Alternating offset U-bend support arrangement |
US11699532B2 (en) | 2018-02-02 | 2023-07-11 | Bwxt Canada Ltd. | Alternating offset U-bend support arrangement |
US11791057B2 (en) | 2018-03-12 | 2023-10-17 | Terrapower, Llc | Reflectors for molten chloride fast reactors |
US11881320B2 (en) | 2019-12-23 | 2024-01-23 | Terrapower, Llc | Molten fuel reactors and orifice ring plates for molten fuel reactors |
US11728052B2 (en) * | 2020-08-17 | 2023-08-15 | Terra Power, Llc | Fast spectrum molten chloride test reactors |
Also Published As
Publication number | Publication date |
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RU2013106699A (en) | 2014-11-10 |
CN102822902A (en) | 2012-12-12 |
US9343187B2 (en) | 2016-05-17 |
CN102822902B (en) | 2016-08-10 |
WO2012047438A1 (en) | 2012-04-12 |
EP2622606A1 (en) | 2013-08-07 |
AR083109A1 (en) | 2013-01-30 |
JP2014510897A (en) | 2014-05-01 |
CA2808425A1 (en) | 2012-04-12 |
TWI549138B (en) | 2016-09-11 |
TW201234387A (en) | 2012-08-16 |
US10803997B2 (en) | 2020-10-13 |
CA2808425C (en) | 2019-02-05 |
KR20130118862A (en) | 2013-10-30 |
US20140321598A1 (en) | 2014-10-30 |
CN106205746A (en) | 2016-12-07 |
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